Layers of the Atmosphere

Layers

• Troposphere• Stratosphere• Mesosphere• Thermosphere• Exosphere

Defining Characteristics

• Thermal (Temperature Changes)• Chemical Composition• Movement• Density• Layers are bound by “pauses” where the

greatest changes in these characteristics occur

Troposphere

• Lowest layer of atmosphere• Next layer above the troposphere is the stratosphere• Border between troposphere and stratosphere is

called the tropopause• Lowest layer of troposphere that touches the Earth

is called the planetary boundary layer

Troposphere

• Contains 75% of the atmosphere’s mass and 99% of its water vapor & aerosols

• Begins at Earth’s surface and extends 4-12 miles

• Almost all weather occurs here• Height varies at equator and poles. At equator,

the height is 11-12 miles. At poles it is under 4 miles. Also varies with season. Low in winter, high in summer.

Traveling up in the Troposphere

• Density of gases decrease with height• The air becomes thinner and colder as you go upward• Water vapor decreases with height (water vapor condenses

out)• Pressure is greatest at sea level and decreases with height

Troposphere Flow

• Wind/weather patterns generally move from west to east (if interrupted, can go from north to south or south to north)

Stratosphere

• Extends around 31 miles above the Earth’s surface (can be 4 to 12 miles)

• Holds 19% of the atmosphere’s gases but very little water vapor

Stratosphere Temperature

• Temperature increases with height

• Heat produced through the process of Ozone formation

• Temperature goes from about -60 deg F (at the tropopause to a max of about 5 deg F at the top of the stratosphere

Temp Divide in the Stratosphere

• Since the air in the stratosphere is warmer at the top of the layer and cooler at the bottom layer, there is no “convection”

• There is no upward movement of gases

• But winds are fast! Moving at 199 mph: “Jet Streams”

Mesosphere

• Extends 31- 53 miles above Earth’s surface• Temp in this layer deceases as altitude

increases• Upper boundary is call the mesopause, the

coldest naturally occurring place on Earth with temps below -226 deg F

Hard to Study the Mesosphere

• Weather balloons and other aircrafts cannot fly high enough to reach the mesosphere

• Satellites orbit above it, cannot directly measure traits

• Use rockets to sample this layer, but flights are brief and infrequent

Mesosphere

• Most meteors vaporize here• Some material from meteors linger so this layer

will have a high concentration of iron and other metals

• Can sometimes have clouds near the poles called “noctilucent clouds”

Thermosphere

• Extends from about 56 miles to a range of 311 to 621 miles

• Right below the exosphere• Boundary between the thermosphere and

exosphere is called the thermopause

The Thermosphere is HOT

• Temperatures climb QUICK in the lower thermosphere, then level off and stay steady with increasing altitude

• Temp is hot due to solar activity• Typically about 360 deg F hotter in daytime

than night• Temps in upper Therm can range from about

932 deg F to 2,000 deg F or higher

Thermosphere to us?

• The thermosphere would feel cold to us, just a little below freezing

• WHY?? The individual air particles can hold a lot of heat BUT they are very few and very far apart

• There’s not enough kinetic energy between those particles to make it seem hot to us

Thermosphere and Space

• Air density is SO low that most of this layer is what we consider outer space

• The space shuttle and International Space Station both orbit Earth in this layer

• X-ray radiation is absorbed here

Thermosphere Waves

• High-energy solar photons strip off electrons from atoms in this layer and create ions

• Just like the ocean, the thermosphere has “waves” and “tides”

• These “waves” and “tides” move the ions around and can create electrical currents

The Aurora

• The “Southern and Northern Lights”

• Charged particles (ions) from space collide with molecules in the thermosphere and “excite” them into a higher energy state

• Those excited molecules shed this excess energy by emitting light

Exosphere

• The most outer layer• Gradually fades into the

vacuum of space• Air is extremely thin, gas

atoms BARELY collide• Basically the same as

outer space

Where does the exosphere start?

• When the sun is active around the peak of the sunspot cycle it can “puff up” the thermosphere, which moves the boundary of where the exosphere starts (thermopause)

• Sometimes the start of the exosphere will be at 620 miles, and sometimes at 310 miles

• So the start really depends on how active the sun is

Is it part of our atmosphere?

• Scientists disagree whether its really a part of the Earth’s atmosphere

• Some think the exosphere is just a part of space

• Other scientists do actually consider it part of our atmosphere

Where does the Exosphere end?

• No clear upper boundary

• Gradually fades into outer space

• Some consider the outermost limit to be at about 120,000 miles, which is about halfway to the moon

Geocorona

• A luminous part of the exosphere that gives off a UV glow

• Caused by the scattering of UV radiation by straggling hydrogen atoms that are barely hanging on by Earth’s gravitational pull

• Occurs at about 62,000 miles

Leaking Atmosphere

• Gas particles in the exosphere sort of travel in curved, arched paths (imagine shooting a cannon ball and it arching back to Earth)

• Particles travel outward but then get arched back in by gravity to be returned to the lower atmosphere

• Some particles are moving too fast to be pulled back in and escape into space